1. Field of the Invention
The present invention relates to purification hearths and, more particularly, to a hearth for refining metals such as titanium by removing high and low density inclusions therefrom.
2. Description of the Invention Background
A variety of different processes and apparatuses have been developed for obtaining relatively pure metals or alloys by separating the slag and burning off or evaporating volatile impurities from the molten metal material. One such apparatus that has been developed to accomplish those tasks is a furnace having an energy source, such as an electron beam gun or a plasma torch, directed toward the surface of the metal in the furnace. Such a furnace, in general, comprises a vacuum chamber with a hearth and crucible system on the floor of the furnace and a number of energy sources mounted above the hearth. The energy sources are used to melt metals introduced onto the hearth and, through sublimation, evaporation and dissolution, remove certain impurities from the molten metal. Additionally, currents created by thermal gradations in the molten metal stream promote inclusion removal. When electron beam sources are utilized, each electron beam can be deflected and scanned over the surfaces of the metal being melted in the hearth. Thereafter, the liquid metal flows from the hearth into the crucible. Energy sources are utilized to maintain the metal in its liquid form as it flows through the hearth to the crucible.
Impurities or inclusions, generally exist within metallic raw materials and can remain within the metal if they are not removed by a refinement process. Those inclusions create areas of potential failure within the metal, and are detrimental in critical applications, such as rotating parts in jet engines. It is important, therefore, when creating high quality metals, that impurities be removed from or dissolved within the metal.
The impurities are generally removed while the metal is in a molten state, when the impurities having varying densities may be removed by settlement or floatation mechanisms. Impurities having a greater density than the metal naturally settle out in the hearth. In a typical process, however, the lower density or neutral density inclusions can be carried into the crucible mold because the lower density or neutral density inclusions are not removed when the metal is poured from the top of a typical hearth.
It is desirable in certain applications for impurities or inclusions that do not settle in the hearth to be sublimated, evaporated or dissolved into the liquid metal to prevent inclusions from forming defects within the solidified metal and thereby creating points of potential failure.
In addition, splatter is created when heat from the energy source impinges on volatile elements within the metal. When splatter occurs, matter, including impurities in the molten stream, can be propelled upward from the surface of the molten stream and outward in all directions. Some of that splatter, therefore, is propelled toward or into the crucible, thereby bypassing at least a portion of the refining process. Thus, it is desirable to reduce or eliminate spattering of the molten stream to prevent such material from by passing the refining process.
Accordingly, a need exists for methods and apparatuses for breaking up inclusions in a stream of molten metal to aid in the removal of impurities from the metal and dissolution of any remaining impurities in the metal.
A need also exists for apparatuses and methods for removing impurities from molten metal, wherein those impurities have a density less than or approximately equal to that of the metal being processed.
There is a further need for apparatuses and methods for preventing matter in a molten metal stream from bypassing further steps in a refining process.
There is still another need for an apparatus having the above-mentioned advantages that is relatively inexpensive to manufacture and install.